Sizing a Mitsubishi Ducted Minisplit
We are replacing a 20+ year old 80% AFUE furnace and 3T A/C with a new ducted mini-split. I’ve interviewed 4-5 different contractors; the local Bryant rep was by far the most interested in asking questions and doing some homework to get us the proper system. This contractor also happens to be a Mitsubishi diamond contractor, and I think we’ve settled on a Mitsubishi M series HP w/ hyper heat coupled with an SVZ fan coil.
My question is related to sizing. Per our attached Manual J, we are looking at a 2.5T or 3T unit. The 2.5T qualifies for $600 in local rebates/tax credits; the 3T has slightly lower efficiency ratings and does not qualify. As I understand, the EER/SEER/HSPF ratings are taken at max btu output, so partial-load efficiency of the 3T unit should be similar to the 2.5T. Is this accurate?
The 3T is way oversized for cooling, but it allows the heat pump to carry our full heating load right down to our design temp. The 2.5T seems to better fit our partial loads in the swing seasons, but it’s latent cooling capacity barely meets the manual J load, and we’ll have to supplement with electric backup heat once temps drop below 5F. Our contractor recommends the 3T due to the humidity removal & higher heating output.
Suggestions on which size is best?
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